docs: auto-document repository features

[codepress-dev]

Summary

• Adds codepress_documentation/ with an initial feature registry (INDEX.md) and per-feature READMEs
• Documents the Django backend that hosts the compiled React SPA and provides auth endpoints (django-spa-backend)
• Documents the Create React App + Redux frontend and its build pipeline into the backend's static directory (react-redux-frontend)
• Documents the unwired reference auth UI components under samples/ (auth-ui-samples)
• Adds a root CLAUDE.md pointing future agents at the feature docs

Test plan

• Reviewed each README against the actual source files for accuracy
• N/A — documentation-only change, no code behavior affected

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Generated by an automated documentation session: https://codepress.dev/dashboard/q5-staging-test/chat/34c44de1-9423-49d4-afba-e3ac02667943